Add OpenTelemetry distributed tracing across HTTP, DB, and Stellar calls

[nanaf6203-bit]

Area: Tracing
Priority: P2 — Medium

Description

For debugging request flows across modules (auth → tips → notifications → Stellar Horizon), distributed tracing via OpenTelemetry reveals bottlenecks and dependencies. No tracing exists today.

Acceptance Criteria

• Install @opentelemetry/api, @opentelemetry/sdk-node, @opentelemetry/auto-instrumentations-node, @opentelemetry/exporter-trace-otlp-http
• Create src/shared/tracing/tracing.ts that initializes SDK with NodeSDK
• Auto-instrument: HTTP, Express, NestJS, TypeORM (pg), undici (for Horizon calls)
• Initialize tracing BEFORE any imports (use --require flag in node command)
• Use OTLP exporter; endpoint from OTEL_EXPORTER_OTLP_ENDPOINT env var
• Add traceparent header propagation on outgoing HTTP requests
• Generate spans for key service methods not covered by auto-instrumentation (e.g. StellarService.verifyPayment)
• Correlation with logging: include traceId in every structured log line
• Add unit test verifying telemetry init with mocked exporter

Technical Notes

• Sampling rate: parentBasedSampler with root sampler configurable
• Resource attributes: service.name=stellartip-backend, service.version, deployment.environment
• Document required OTEL_* environment variables in README

[gloskull]

Hello, I have 4 years of experience delivering solutions for projects like this, covering backend, frontend, and smart contract development. After carefully reviewing your requirements, I have a clear understanding of the task and am confident in my ability to deliver a clean, efficient, and thoroughly tested solution on time. I prioritize code quality, maintainability, and industry best practices throughout the development process.